FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] This gene encodes a member of a family of transcription factors that heterodimerize with E2F proteins to enhance their DNA-binding activity and promote transcription from E2F target genes. The encoded protein functions as part of this complex to control the transcriptional activity of numerous genes involved in cell cycle progression from G1 to S phase. Alternative splicing results in multiple transcript variants. Pseudogenes of this gene are found on chromosomes 1, 15, and X.[provided by RefSeq, Jan 2009] PHENOTYPE: Homozygotes for a targeted null mutation exhibit reduced expansion of the ectoplacental cone and chorion, small yolk sacs, and impaired endoreduplication in trophoblast giant cells. Mutants die by embryonic day 12.5. [provided by MGI curators]